From 04df472194e194559d33619e089f3aa918e3f5a2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Pedro?= <jpedrolmail@gmail.com>
Date: Thu, 9 Feb 2023 03:10:19 +0000
Subject: [PATCH 1/2] Added unit test for #10226.

---
 .../Styling/StyledElementTests_Theming.cs     | 40 ++++++++++++++++---
 1 file changed, 35 insertions(+), 5 deletions(-)

diff --git a/tests/Avalonia.Base.UnitTests/Styling/StyledElementTests_Theming.cs b/tests/Avalonia.Base.UnitTests/Styling/StyledElementTests_Theming.cs
index b5a9b35134..60603937d9 100644
--- a/tests/Avalonia.Base.UnitTests/Styling/StyledElementTests_Theming.cs
+++ b/tests/Avalonia.Base.UnitTests/Styling/StyledElementTests_Theming.cs
@@ -104,7 +104,7 @@ public class StyledElementTests_Theming
             target.Theme = null;
             Assert.Equal("style", target.Tag);
         }
-        
+
         [Fact]
         public void TemplatedParent_Theme_Is_Detached_From_Template_Controls_When_Theme_Property_Cleared()
         {
@@ -539,12 +539,42 @@ public class StyledElementTests_Theming
             Assert.Same(target.Theme, theme3);
         }
 
+        [Fact]
+        public void TemplatedParent_Theme_Change_Applies_To_Children()
+        {
+            var theme = CreateDerivedTheme();
+            var target = CreateTarget();
+
+            Assert.Null(target.Theme);
+            Assert.Null(target.Template);
+
+            var root = CreateRoot(target, theme.BasedOn);
+
+            Assert.NotNull(target.Theme);
+            Assert.NotNull(target.Template);
+
+            root.Styles.Add(new Style(x => x.OfType<ThemedControl>().Class("foo"))
+            {
+                Setters = { new Setter(StyledElement.ThemeProperty, theme) }
+            });
+
+            root.LayoutManager.ExecuteLayoutPass();
+
+            var border = Assert.IsType<Border>(target.VisualChild);
+            Assert.Equal(Brushes.Red, border.Background);
+
+            target.Classes.Add("foo");
+            root.LayoutManager.ExecuteLayoutPass();
+
+            Assert.Equal(Brushes.Green, border.Background);
+        }
+
         private static ThemedControl CreateTarget()
         {
             return new ThemedControl();
         }
 
-        private static TestRoot CreateRoot(Control child)
+        private static TestRoot CreateRoot(Control child, ControlTheme? theme = null)
         {
             var result = new TestRoot()
             {
@@ -552,7 +582,7 @@ public class StyledElementTests_Theming
                 {
                     new Style(x => x.OfType<ThemedControl>())
                     {
-                        Setters = { new Setter(StyledElement.ThemeProperty, CreateTheme()) }
+                        Setters = { new Setter(StyledElement.ThemeProperty, theme ?? CreateTheme()) }
                     }
                 }
             };
@@ -580,8 +610,8 @@ public class StyledElementTests_Theming
             {
                 new Style(x => x.Nesting().Template().OfType<Border>())
                 {
-                    Setters = 
-                    { 
+                    Setters =
+                    {
                         new Setter(Border.BackgroundProperty, Brushes.Red),
                         new Setter(Control.TagProperty, tag),
                     }

From b8a987e84748b3c26d37dbfa787e720c0a188aed Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Pedro?= <jpedrolmail@gmail.com>
Date: Wed, 8 Feb 2023 20:29:25 +0000
Subject: [PATCH 2/2] Ensure templated parent control theme is applied.

---
 src/Avalonia.Base/Layout/Layoutable.cs | 6 ++++++
 src/Avalonia.Base/StyledElement.cs     | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/Avalonia.Base/Layout/Layoutable.cs b/src/Avalonia.Base/Layout/Layoutable.cs
index 775b8adddd..c45fc16929 100644
--- a/src/Avalonia.Base/Layout/Layoutable.cs
+++ b/src/Avalonia.Base/Layout/Layoutable.cs
@@ -795,6 +795,12 @@ namespace Avalonia.Layout
             InvalidateMeasure();
         }
 
+        internal override void OnTemplatedParentControlThemeChanged()
+        {
+            base.OnTemplatedParentControlThemeChanged();
+            InvalidateMeasure();
+        }
+
         /// <summary>
         /// Called when the layout manager raises a LayoutUpdated event.
         /// </summary>
diff --git a/src/Avalonia.Base/StyledElement.cs b/src/Avalonia.Base/StyledElement.cs
index 5bf022cd51..b910012444 100644
--- a/src/Avalonia.Base/StyledElement.cs
+++ b/src/Avalonia.Base/StyledElement.cs
@@ -390,7 +390,7 @@ namespace Avalonia
         /// </returns>
         public bool ApplyStyling()
         {
-            if (_initCount == 0 && (!_stylesApplied || !_themeApplied))
+            if (_initCount == 0 && (!_stylesApplied || !_themeApplied || !_templatedParentThemeApplied))
             {
                 GetValueStore().BeginStyling();